Summertime heat is forecast to become even deadlier without action to drastically reduce the greenhouse gas emissions that cause climate change, according to a new study.
Under the Paris climate agreement, 195 countries pledged to cut their greenhouse gas in an effort to hold global warming to two degrees Celsius, or 3.6 degrees Fahrenheit, above preindustrial levels. They also promised efforts to limit the temperature increase even further, to 1.5 degrees Celsius.
The half-degree difference between 1.5 and two degrees may not seem like much, but, according to research published Wednesday in the journal Science Advances, it could mean saving or losing thousands of lives each year in the United States alone.
The researchers wanted to assess the benefits of the Paris Agreement “not in terms of the climate or the temperature, but in terms of how many human lives could be saved or how many heat-related deaths could be avoided by mitigating climate change,” said Eunice Lo, a research associate at the University of Bristol and lead author of the study.
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Dr. Lo and her colleagues used the 1.5 degree Celsius temperature target from the Paris Agreement as their baseline, and under that level of warming estimated the heat deaths that would occur in 15 cities across the United States. They selected those cities — which included Detroit, Los Angeles, Philadelphia and New York — because there was reliable climate and health data available.
Once they had that baseline, they compared what would happen if the planet reached two degrees Celsius of warming by the end of this century. Despite growing awareness of climate change, the world, which has already by warmed roughly one degree Celsius, is on target to hit three degrees Celsius of warming by century’s end. The researchers looked at what would happen under that warming scenario, as well.
What they found is that, in almost every city they considered, the more global temperatures rose, the more people will die. The exceptions were Atlanta and San Francisco, a finding that researchers attributed to limited extreme heat days in the data for those cities. The greatest risks were in northern cities like Philadelphia, New York and Boston.
“The more warming you have, the more heat waves you have,” said Michael Wehner, a senior staff scientist in the computational research group at Lawrence Berkeley National Laboratory, who was not involved in this study. “The more heat waves you have, the more people die.”
More on the risks of extreme heat
“The numbers are quite astonishing in terms of how many deaths we could afford by limiting global warming to 1.5 degrees from three degrees,” Dr. Lo said. For example, she said, that would allow New York City to avoid 2,716 heat-related deaths during the most extreme temperature years.
There are some caveats. For example, as temperatures warm people tend to adapt. The 2003 heat wave in Europe is a good example. That year, an estimated 1,050 people died in London and Paris because of soaring temperatures. So many people died in France that summer that morgues and funeral homes ran out of space. But in 2010, even though similar temperatures hit Europe, far fewer people in Western Europe died. (An estimated 56,000, however, died in Russia.)
“People become aware of the dangers,” Dr. Wehner said. “They changed their behaviors so that they were more likely to survive.”
A key form of adaptation is air-conditioning. But in cities like Seattle, where heat mortality is expected to increase, only a third of residents have air-conditioners. And air-conditioners pose their own problems both as contributors to climate change through energy consumption and because they pump warm air outside, further increasing urban temperatures. And, there’s the grim fact that often it takes a catastrophic heat wave before cities put in place measures, like public cooling centers, that help residents to cope.
“The people that are at risk in cities are the very young, the very ill, and, generally, the poor,” Dr. Wehner said. “It’s people who don’t have access to air-conditioning.”
That does not always mean older people in cities. Dr. Wehner noted, for example, that in the central parts of California, those most at risk are Hispanic men in their 50s. They tend to be farm laborers, and farm fields and construction sites offer little respite from hot weather.
Kendra Pierre-Louis is a reporter on the climate team. Before joining The Times in 2017, she covered science and the environment for Popular Science. @kendrawrites
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